In rotors used in permanent magnet type motors used as power sources for automobiles, various kinds of techniques have been proposed in order to improve characteristics relating to durability, cost, magnetic efficiency, heat dissipation, and connection strength between a rotor yoke and a permanent magnet, etc., in accordance with intended use.
In the above rotors for permanent magnet type motors, for example, a technique has been proposed, in which a permanent magnet is embedded in a rotor yoke so as to improve durability (for example, see Japanese Unexamined Patent Application Publication No. Hei 6-38415). A technique has been proposed, in which a rotor yoke and a permanent magnet are connected to each other by sintering so as to improve magnetic efficiency and heat dissipation (for example, see Japanese Unexamined Patent Application Publication No. Hei 7-177712). A technique is proposed, in which a rotor yoke and a permanent magnet are connected by using an adhering technique by polymer material so as to reduce the cost and improve the connection strength therebetween (for example, see Japanese Unexamined Patent Application Publication No. 2002-272033).
However, in the rotor disclosed in the above Japanese Unexamined Patent Application Publication No. Hei 6-38415, a rotor is relatively high in cost since the rotor yoke is disposed between permanent magnets so that the rotor is double in radius, and magnetic efficiency based on air gap between the rotor and a stator is low since the permanent magnet is not exposed on a surface of the rotor. In the rotor disclosed in the above Japanese Unexamined Patent Application Publication No. Hei 7-177712, the rotor is relatively high in cost due to manufacturing equipment used in a powder metallurgy method, the connection strength at high temperature and at high speed rotation and the durability including thermal shock are low since sintering connection without an adhering medium is adopted, and manufacturing cannot be performed when the yoke has a stacked structure since a powder metallurgy method cannot be applied thereto. In the rotor disclosed in the above Japanese Unexamined Patent Application Publication No. 2002-272033, the durability of the rotor is lowered since adhesives composed of a polymer are softened at temperatures during the use of the rotor, and heat dissipation from the permanent magnet to the rotor yoke is low since adhesives for permanent magnet have thermal conductivity lower than metal films, so that heat does not dissipate to a side of the rotor. In the rotor disclosed in the above Japanese Unexamined Patent Application Publication No. 2002-272033, when the adhesives composed of the polymer material are used, magnetic efficiency based on air gap between the rotor and a stator and magnetic efficiency based on the included gap between the permanent magnet and the rotor yoke are low.
Therefore, in recent years, techniques have been required such that all characteristics regarding the durability, the cost, the magnetic efficiency based on the air gap between the rotor and the stator, the magnetic efficiency based on the included gap between the permanent magnet and the rotor yoke, the heat dissipation, and the connection strength between the rotor yoke and the permanent magnet favorably reach high levels.